Various apparatus for the feeding or advancement of edgeperforated paper webs into or through printers, such for example as dot-matrix printers, are known in the art. In a commonly-employed arrangement, the feeding force is transmitted to the web by a drive belt that carries, on its outwardly-disposed surface brought into opposition with the web, a plurality of pins for engagement with the transverse edge-defined web perforations. These pins may advantageously be configured so as to have a diameter that gradually increases in the direction of the pin base. The inward or opposite surface of the belt is provided with a series of teeth that are engageable with corresponding tooth gaps or indentations in a rotatably driven wheel through which the belt is thereby driven by the wheel. The paper web, thus advancingly carried on the upper or outward face of the belt, is thereby stretched transverse to the axis of the diametrically-varying pin and/or is pressed transverse to the pin axis by a swingable tractor flap.
Such drive belts are often used in so-called tractors which, arranged in pairs proximate the perforated edge regions of so-called Leporello paper, enable relatively precise feeding of the paper web. Such precision requires, of course, accurate engagement of the pins of the drive belt with the edge perforations in the web. However, the use of these web perforations for accurate paper feeding is fully effective only where the pins, when disposed in the perforations, fill the perforations in their entirety--i.e. the pins have a maximum diameter at their bases that substantially corresponds to the perforation diameter. Nevertheless, here too there remain differences in the effectiveness of transmission of the web feeding force. It must be recognized that the forces imparted to the opposed edge strips of the Leporello paper must be transmitted simultaneously and in the same amount in order to avoid skewed feeding of the web. Furthermore, transmission of the feeding force is dependent on the overall frictional conditions between the belt and web since the paper, together with the perforated edge strips thereon, must during transport be moved first onto the pins and, then, off and away from them.
Drive belts of this type having pins at fixed spacings or distances apart along the upper side or face thereof and the aforementioned teeth on the lower side or face of the belt are disclosed, for example, in Federal Republic of Germany OS 36 14 981 and U.S. Pat. No. 4,130,230. Such belts are typically disposed in pairs which are spaced apart by the width of the paper web and are concurrently operated so as to provide uniform travel of the two tractors in which the belts are respectively located.